FIGS. 11 and 12 illustrate a tilt-telescopic steering apparatus disclosed in Patent Document 1. The steering apparatus has a steering shaft 2 having a rear end portion to which a steering wheel 1 is fixed, a steering column 3 rotatably supporting the steering shaft 2 therein, a steering force assist device 5 which applies assist torque to the steering shaft 2 using an electric motor 4 as an auxiliary power source, and a steering gear unit 7 which pushes or pulls tie-rods 6, 6 in accordance with a rotation of the steering shaft 2. In this description, a front-rear direction means a front-rear direction of a vehicle.
The steering shaft 2 has an inner shaft 8 and an outer shaft 9. The inner shaft 8 and the outer shaft 9 are combined to transmit a rotational force and to be relatively displaced in an axial direction. A front end portion of the inner shaft 8 is connected to an input shaft of the steering force assist device 5 in a gear housing 10 of the steering force assist device 5. The steering column 3 has an inner column 11 and an outer column 12. A front end portion of the outer column 12 is fitted to a rear end portion outer side of the inner column 11 so that it can be relatively displaced in the axial direction. The inner column 11 is supported to a vehicle body 14 by a front fixed bracket 13 via the gear housing 10. The fixed bracket 13 swingably supports the gear housing 10 and the steering column 3 about a pivot pin 15. The front end portion of the outer column 12 is supported to the vehicle body 14 by a rear fixed bracket 17.
The fixed bracket 17 is supported to the vehicle body 14 so that it is forwards separated when a strong forward shock is applied. As shown in FIG. 12, the fixed bracket 17 has left and right side wall portions 18, 18 and support plate parts 19, 19 that are provided at upper end portions of the side wall portions 18, 18. Notches 20, 20 are provided for the support plate parts 19, 19 such that they are opened towards rear end edges of the support plate parts 19, 19. The notches 20, 20 are engaged with capsules 21, 21. The capsules 21, 21 are fixed to the vehicle body 14 by bolts (not shown).
Upon a collision accident, a high forward shock load is applied from a driver body to the steering column 3 via the steering wheel 1 and the steering shaft 2. The steering shaft 2 and the steering column 3 absorb this shock energy, and at the same time cause reduction in the entire length. As a result, the fixed bracket 17 is forwards displaced together with the outer column 12 and is thus forwards separated relative to the vehicle body 14, thereby permitting the steering wheel 1 to be forwards displaced.
In order to adjust front-rear and upper-lower positions of the steering wheel 1, the outer column 12 is supported to the fixed bracket 17 so that it can be moved in front-rear and upper-lower directions. A pair of clamped portions 23, 23 forming a movable bracket 22 is integrated with the outer column 12 on a lower surface of the front end portion of the outer column 12. Column side through-holes 24, 24 elongated in the front-rear direction are formed through the clamped portions 23, 23, respectively, at locations aligned with each other. Vehicle body side through-holes 25, 25 elongated in the upper-lower direction are formed through a portion of the side wall portions 18, 18 at locations aligned with each other. A rod member 26 is inserted into the column side through-holes 24, 24 and the vehicle-side through-holes 25, 25 from one side to the other side (from the right to the left in FIG. 12). An adjusting nut 28 is screwed to an end of the other side of the rod member 26 so that the clamped portions 23, 23 are held by the side wall portions 18, 18, and is configured so that it can be rotated by an adjusting lever 27.
Therefore, by rotating the adjusting nut 28 on the basis of an operation of the adjusting lever 27 to thus change an interval between the adjusting nut 28 and a head part 29 of the rod member 26, it is possible to fix the outer column 12 to the fixed bracket 17 or to release the outer column from the fixed bracket 17 and to fix the outer column 12 to the inner column 11 or to release the outer column from the inner column 11. In a state in which the interval between the adjusting nut 28 and the head part 29 is widened, it is possible to move the outer column 12 forwards and rearwards (to displace the outer column relative to the inner column 11) within a range (a telescopic adjusting range) in which the rod member 26 can be displaced in the respective column side through-holes 24, 24, thereby adjusting the front-rear position of the steering wheel 1. Furthermore, it is possible to move the steering column 3 upwards and downwards within a range (a tilt adjusting range) in which the rod member 26 can be displaced in the respective vehicle body side through-holes 25, 25, thereby adjusting the upper-lower position of the steering wheel 1. That is, at the state where the interval between the adjusting nut 28 and the head part 29 is widened, it is possible to adjust the front-rear and upper-lower positions of the steering wheel 1 within the ranges in which the rod member 26 can be displaced in the respective column side through-holes 24, 24 and the respective vehicle body side through-holes 25, 25.
A front end portion of an output shaft 16 of the steering force assist device 5 is coupled to a rear end portion of an intermediate shaft 31 via a universal joint 30. A front end portion of the intermediate shaft 31 is coupled to an input shaft 33 of the steering gear unit 7 via a separate universal joint 32. The tie-rods 6, 6 are pushed or pulled in connection with rotation of the input shaft 33, so that a desire steering angle is applied to the steering wheel.
When manufacturing the outer column 12 as described above, an outer column main body is first molded by a die-casting using a lightweight alloy such as aluminum alloy. Then, an inner peripheral surface of the outer column main body is subject to cutting work and is thus finished. For the steering apparatus, the cutting work for finishing an inner diameter of the outer column 12 with accuracy is troublesome and the processing cost is thus increased. Also, the inner peripheral surface of the outer column 12 and an outer peripheral surface of the inner column 11 are fitted over an entire circumference. Thus, when the inner diameter precision of the outer column 12 is not sufficient, a partial contact is caused, so that the inner column 11 cannot be stably maintained.
Thus, as shown in FIG. 13, Patent Document 2 discloses a telescopic steering apparatus in which protuberances 34, 34 protruding radially inward from an inner peripheral surface of an outer column are formed at a plurality of positions along a circumferential direction on the inner peripheral surface of the outer column 12a, and distal ends (radially inner end portions) of the respective protuberances 34, 34 contact an outer peripheral surface of an inner column 11a in an assembled state. When manufacturing the outer column 12a, an outer column main body is first molded by the die-casting. After that, forging and broaching are performed on a portion of an inner peripheral surface of the outer column main body overlapping the outer peripheral surface of the inner column 11a at a plurality of locations (eleven locations in the illustrated example) along a circumferential direction, thereby forming the respective protuberances 34, 34.
In the case of the outer column 12a as described above, the cutting work (the broaching and the like) is preferably performed only for the distal ends of the respective protuberances 34, 34. Therefore, compared to a configuration where the cutting work is performed for the entire inner peripheral surface of the outer column, it is possible to reduce the processing cost. However, the method of forming the outer column 12a and the method of the protuberances 34, 34 are different from each other. Hence, it takes much time to perform the processing and the processing cost is thus increased. Also, in order to stably support the inner column 11a radially inside the outer column 12a without partial contact or play, the contacting conditions of all the protuberances 34, 34 and the outer peripheral surface of the inner column 11a are preferably the same. However, when the multiple protuberances 34, 34 are provided, like the outer column 12a, the process for making the contacting conditions be the same is troublesome.
FIG. 14 shows another outer column 12b disclosed in Patent Document 2. An inner peripheral surface of the outer column 12b is formed with support pawls 35, 35 at three circumferential positions facing an outer peripheral surface of an inner column 11b in an assembled state. The respective support pawls 35, 35 are formed by performing press processing for the outer column 12b and further bending processing from the inner peripheral surface of the outer column 12b radially inwards. The outer peripheral surface of the outer column 12b is provided with a movable bracket 22a at a part thereof in an axial direction. The movable bracket 22a has left and right clamped portions 23a, 23a. Each of the clamped portions 23a, 23a is formed by bending a plate-shaped material and has one end continuing from the outer peripheral surface of the outer column 12b and the other end welded to the outer peripheral surface of the outer column 12b. 
In the case of the outer column 12b, the support pawls 35, 35 are formed at the three positions that are spaced at a substantially equal interval in the circumferential direction. Therefore, it is possible to easily perform the process for making the contacting conditions of distal ends of all the support pawls 35, 35 and the outer peripheral surface of the inner column 11b be the same. However, each of the support pawls 35, 35 has a cantilever-shaped structure where it is bent radially inwards from the inner peripheral surface of the outer column 12b. Hence, it is difficult to secure the stiffness for stably supporting the inner column 11b radially inside the outer column 12b. Also, the operation of welding the other end of the clamped portions 23a, 23a to the outer column 12b consumes much time, which increases the processing cost.
Patent Documents 1, 3 and 4 disclose a structure where an energy absorption member for absorbing a shock load by plastic deformation is provided between a steering column (or a member fixed to the steering column) and a vehicle body (or a member fixed to the vehicle body) so as to alleviate shock, which is applied to a driver body upon a secondary collision, and to thus protect the driver, in addition to a structure of supporting the steering column to the vehicle body so that it can be forwards separated. According to the structure of the related art, since the separate energy absorption member is provided, the component manufacturing, the component management and the assembling operation are troublesome, which increases the cost. Patent Document 5 discloses a technology of perforating a column during hydro forming process.